Clockspring using resettable fuse for heated steering wheel

ABSTRACT

A clockspring for powering a heated steering wheel having a resettable fuse connected in series between the heating element and a power source for the heating element. When a predetermined current limit is exceeded the resettable fuse trips and breaks the circuit providing power to the heating element. After the resettable fuse cools, the resettable fuse automatically reestablished the connection between the heating element and the power source for the heating element. The resettable fuse can be easily and economically implemented into a conventional clockspring, thus enabling a conventional clockspring to provide electrical connections for high current devices, such as a steering wheel heating element. Moreover, the present invention provides a reliable and cost effective safety device for preventing damage to the clockspring and the vehicle, and serious injury to a driver or a passenger.

FIELD OF THE INVENTION

The present invention relates generally to clocksprings for steeringcolumns on automotive vehicles, and more particularly, to a clockspringhaving a resettable fuse.

BACKGROUND OF THE INVENTION

An increasing number of automobiles have air bag crash systems. The airbag is typically located on the steering wheel facing the driver. Theair bag must be in continuous electrical connection with impact sensorsin the car body. In the event of a crash, the impact sensor or sensorsprovide an electrical signal to the air bag crash assembly thatinstantly inflates the air bag. Accordingly, there is an essential needfor a reliable electrical connection between the rotatable portion ofthe air bag assembly, which is mounted to the steering wheel, and theremaining portion of the assembly, which is mounted to the stationarysteering column.

Electrical connections between rotatable and stationary parts arewell-known. Typically, an electrical brush rests upon a conductive ring,with one of the parts being rotatable to provide a rotatable electricalconnection. However, there is a risk, particularly during the impact ofan accident, of transient failure of the electrical connection in thebrush and ring system, which could result in failure of the entire airbag system crash assembly.

Accordingly, a clockspring has been previously developed. Theclockspring typically includes a flat, flexible, ribbon cable woundaround a rotatable hub. The rotatable hub is located on the steeringcolumn. The ribbon cable is contained within a housing. A first end ofthe ribbon cable is connected to a deployment unit of the air bag and asecond end of the ribbon cable is connected to interconnectors whichpass out of the housing. The interconnectors are connected to the impactsensor or sensors on a stationary location of the vehicle. In thismanner, the deployment unit for the air bag is reliably connected to theimpact sensors of the vehicle.

As discussed above, clocksprings were originally developed to provide areliable connection between the steering wheel and the steering columnfor airbags. As clocksprings continue to develop, more and moreaccessory and instrument controls are being located upon the steeringwheel and, as a result, are utilizing the clockspring for electricalconnections to the steering column. These additional components areincreasing the number of individual signal lines contained within theribbon cable. Moreover, the electrical current requirements forindividual signal lines are also increasing due to some of the highcurrent devices being incorporated into the steering wheel.

Consumers continue to desire more and more comfort features with theirautomobiles. For example, one high current device or feature that maypossibly be added to the steering wheel is a heating element. Aconventional clockspring is not designed to handle such a high currentdevice. Conventional practice would be to utilize a slip ring totransmit high electrical current between a steering wheel and a steeringcolumn. Unfortunately, slip rings have a tendency to generateunacceptable noise levels. Furthermore, slips rings wear over timecausing degradation in performance.

Since clocksprings typically utilize thin ribbon cables with lowamperage wiring, it can be potentially dangerous for high currents toflow through clocksprings. An uncontrolled high current in a clockspringcould damage the vehicle and its instruments. Furthermore, resultingdamage to the clockspring could likely defeat a major purpose of theclockspring: providing a reliable electrical connection for the airbagsafety system. Moreover, such an uncontrolled current could cause a firedamaging the vehicle and seriously injuring a driver or passenger.

Accordingly, there is a need for a system of monitoring and controllinghigh current devices that utilize clocksprings.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to enable conventionalclocksprings, with a slight modification, to safely handle high currentdevices.

Another object of the present invention is to monitor current flowthough clocksprings of high current devices.

An additional object of the present invention is to enable aconventional clockspring to be modified at a minimal cost in order tohandle high current devices.

A further object of the present invention is to enable a clockspring torecover automatically if a high current threshold through theclockspring is exceeded.

Moreover, a specific object of the present invention is to enable aclockspring to provide an electrical connection for a heating element ina heated steering wheel.

In accordance with the present invention, a clockspring for powering aheated steering wheel is provided having a resettable fuse connected inseries between the heating element and a power source for the heatingelement. When a predetermined current limit is exceeded the resettablefuse trips and breaks the circuit providing power to the heatingelement. After the resettable fuse cools, the resettable fuseautomatically reestablishes the connection between the heating elementand the power source for the heating element. The resettable fuse can beeasily and economically implemented into a conventional clockspring,thus enabling a conventional clockspring to provide electricalconnections for high current devices, such as a steering wheel heatingelement. Moreover, the present invention provides a reliable and costeffective safety device for preventing damage to the clockspring and thevehicle, and serious injury to a driver or passenger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a clockspring configured in accordance withthe present invention;

FIG. 2 illustrates a flexible ribbon cable configured in accordance withthe present invention;

FIG. 3 is a cut-away view of the clockspring illustrating a resettablefuse incorporated into the substrate of the clockspring;

FIG. 4 is a circuit diagram of one embodiment of the present invention;and

FIG. 5 is a cross-sectional view of a resettable fuse that may beutilized in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 shows a cross-sectional view of aclockspring 10 configured in accordance with the present invention. Theclockspring 10 includes a frame 12 having a housing 14. The frame 12includes mounting brackets 16 having mounting holes 18. The inside ofthe housing 14 is lined by a radial wall 20 and an inner back 22. Arotatable hub 24 is located in the center of the clockspring 10. Therotatable hub 24 includes a backbone 26 for securing a first end 28 of aribbon cable 32. An aperture 30 is located at the center of theclockspring 10 to enable the clockspring 10 to be placed around asteering column of an automobile. The ribbon cable 32 is flexible and iswrapped around the hub 24 enough times so as to enable a steering columnto be rotated as many times as necessary to turn the front wheels of avehicle from a complete left turn to a complete right turn.

FIG. 2 illustrates the ribbon cable 32 separate from the clockspring 10.The ribbon cable 32 is relatively flat and contains numerous individualsignal lines or channels 34, which are individual, insulated wires. Inthe illustrated embodiment there are eight signal lines 34. Of course,different embodiments of the present invention can comprise more or lesssignal lines 34 within the ribbon cable 32. The first end 28 of theribbon cable 32 is attached to a connector plug 36 which is configuredto plug into the backbone 26 of the hub 24. The plug 36 includes metalprongs 37. The second end 38 of the ribbon cable 32 has exposed signalline wires 40 which are to be connected to contacts 42 (FIG. 1).

Referring back to FIG. 1, the exposed signal line wires 40 of the ribboncable 32 are connected to contacts 42. Contacts 42 are preferably copperleads that are electrically connected to connection lines or conductivetraces 44 in a substrate 46 of the clockspring 10. The conductive traces44 are preferably copper filaments etched into the substrate 44. Theconductive traces 44 are visible through cut-aways 43 and 45 in thesubstrate 46. Contacts 48 are electrically connected to opposing ends ofthe conductive traces 44. The contacts 48 are preferably copper tabs orstrips that may be inserted into a plug or other electrical receptacle.

Each conductive trace 44 corresponds to a specific channel 34 in theribbon cable 32. The signal lines 34 may carry electrical signal fornumerous devices on a steering wheel of an automobile. For example,these devices may include cruise control, turn signal control,windshield wiper control, horn control, and or course, deploymentsignals for an air bag crash system. Furthermore, the signal lines 34may also communicate signals for high current devices such as a heatingelement for a steering wheel. A heating element for a steering wheelcould draw current over 10 amperes. Left unrestricted or unmonitored, ahigh current could seriously damage the clockspring, the vehicle, andeven injure the driver or passenger.

In accordance with the present invention, a resettable fuse iselectrically connected in series on each of the signal lines ofclockspring that may potentially draw an undesirably high current. If apredetermined current is exceeded, the resettable fuse temporarilyterminates the electrical connection for that signal line to preventdamage. In accordance with a further feature of the present invention,the resettable fuse automatically reconnects a previously terminatedconnection after a period of time, thereby eliminating a need for anycostly and burdensome manually maintenance to replace the fuse orreestablish a terminated connection.

FIG. 1 illustrates a resettable fuse 50 electrically connected toconductive trace 52 (shown in shadow and cut-away 54). Conductive trace52 electrically connects specific connector lead 56 of connector 41 withspecific contact lead 60 of connector plug 58. Plug 58 includes contacts60 and 62 which may be connected to an electrical receptacle.

In the illustrated embodiment of FIG. 1, the signal line 34 connected toconductive trace 52 is designed to carry and monitor current for a highcurrent device. In accordance with the invention, a conventionalclockspring may be modified to handle a high current device at minimalcosts by incorporating a resettable fuse into the necessary signal lineof a clockspring. When the current on signal line 52 exceeds apredetermined limit, or temperature if desired, the resettable fuse 50trips and breaks the electrical connection on conductive trace 52. Aftera period of time, or after the temperature of the resettable fuse 50cools, the resettable fuse 50 automatically reestablishes the electricalconnection of conductive trace 52.

FIG. 3 illustrates another embodiment of the present invention. Asubstrate 66 is shown having nine conductive traces 71, 72, 73, 74, 5,76, 78 and 79. The substrate 66 is secured to a rigid mounting board orbase 67 of a clockspring. The mounting board 67 may be configured ofplastic, metal, or other appropriate material. The conductive traces71-79 are shown in a cut-away 80 of the substrate 66. The conductivetraces 71-79 are electrically connected to contact leads 82-90, whichare preferably composed of copper. The contact leads 82-90 are locatedon a plug 92 which is to be inserted into an appropriate socket orreceptacle. A resettable fuse 94 is shown connected in series onconductive trace 75.

FIG. 4 illustrates a block circuit diagram 96 of a further embodiment ofa clockspring according to the present invention. In this embodiment theclockspring has seven signal lines 101-107. A block diagram of a flatribbon cable 97 is shown. Air bag signal lines 101-104 are illustrated,and signal line 105 corresponding to a vehicle horn is also illustrated.Illustrated signal lines 106 and 107 correspond to a heated steeringwheel element. A resettable fuse 98 is shown connected in series onsignal line 106.

FIG. 5 is a cross-sectional view of one embodiment of a resettable fuse110 that may be utilized in the present invention. The resettable fuse110 is formed into a substrate 112 and includes a fuse section 114 incontact with opposing electrical terminals 116 and 118. The fuse section114 may be formed of a reaction material such as polyethylene glycol anda diepoxide. The terminals 114 and 116 may be formed from silver-filledepoxy resin. A detailed explanation of a resettable fuse that may beused in the present invention is provided in U.S. Pat. No. 5,963,121,issued to Stygar et al. on Oct. 5, 1999, which is hereby incorporated byreference.

It is to be understood that the foregoing description is merely adisclosure of particular embodiments and is no way intended to limit thescope of the invention. Other possible modifications will be apparent tothose skilled in the art, all of which are intended to be covered by thefollowing claims:

We claim as our invention:
 1. A clockspring for a steering column of avehicle, comprising: a housing; a rotatable hub mounted to the housingfor winding a ribbon cable; a substantially flat ribbon cable, wherein afirst end of the substantially flat ribbon cable is connected to the huband a second end of the substantially flat ribbon cable is connected tothe housing; a first signal line having a portion contained within thesubstantially flat ribbon cable; and a resettable fuse mounted to thehousing and connected in series to the first signal line.
 2. Theclockspring of claim 1, the ribbon cable further comprising: at least asecond signal line.
 3. The clockspring of claim 1, the housing furthercomprising: a first connector, proximate to the second end of the ribboncable, for connecting the first signal line to the housing.
 4. Theclockspring of claim 3, the housing further comprising: a substrate forsecuring the first connector and the fuse to the housing, the substratecomprising at least one conductive trace and a second connector, whereinthe at least one conductive trace provides an electrical connectionbetween the first connector and the second connector.
 5. The clockspringof claim 4, wherein the fuse is connected in series between the firstand second connector via the at least one conductive trace.
 6. Theclockspring of claim 5, wherein the fuse is disposed on the substrate.7. The clockspring of claim 6, wherein the fuse is resettable and a fusesection of the resettable fuse is comprised of a mixture of reactionproduct of polyethylene glycol and diepoxide.
 8. The clockspring ofclaim 7, wherein the at least one conductive trace is composedessentially of copper disposed on the substrate.
 9. The clockspring ofclaim 1, wherein the resettable fuse is connected in series between thehub and the first end of the ribbon cable.
 10. The clockspring of claim1, the ribbon cable further comprising multiple signal lines.
 11. Theclockspring of claim 1, wherein the first signal line carries electricalsignals to a heating element in a steering wheel of a vehicle.
 12. Theclockspring of claim 1, further comprising: a plug having at least oneprong electrically connected to the resettable fuse, the plug beingconnected proximate to an end of the ribbon cable, and the resettablefuse being located with the plug.
 13. The clockspring of claim 1,wherein the resettable fuse is located in the hub.
 14. A clockspring fora steering column of a vehicle, comprising: a housing; a hub rotatablyattached to the housing; a ribbon cable having multiple signal linesproviding electrical connections between the housing and hub, wherein atleast one signal line is to be connected to a heating device in thesteering wheel of a vehicle; a resettable fuse connected in series withthe at least one signal line and positioned electrically between theheating device in the steering wheel and a power source for the heatingdevice; and wherein tripping said resettable fuse terminates currentflow in the at least one signal line, and after a period of time, saidresettable fuse automatically resets, thus enabling current to flow inthe at least one signal line.
 15. A method of supplying high current toa heating element in a steering wheel of a vehicle via a clockspringribbon cable, comprising the steps of: defining an acceptable currentlimit to be carried over a signal line of a clockspring ribbon cablebetween a power source on a column side of a steering wheel and aheating element in a steering wheel; passing current signals over thesignal line and through a resettable fuse connected in series betweenthe power source and the heating element; exceeding the acceptablecurrent limit over the signal line; tripping the resettable fuse as aresult of the acceptable current limit being exceeded, and therebybreaking an electrical connection provided by the signal line; andreestablishing automatically the electrical connection provided by thesignal line after a period of time when the resettable fuse resetsitself.